The present invention generally relates to the stirring of a substance in a container and the metering of quantities of such substance from the container. More specifically, the present invention relates to the design of the stirring element or agitator used to stir substances in containers.
Liquid metering systems are used in a wide variety of applications in the pharmaceutical industry, such as for injecting metered doses of viscous or concentrated suspensions or slurries onto or into substrates and other drug containment media. FIG. 1 illustrates an example of a recently developed liquid metering device in the form of a liquid metering gun generally designated 10. Metering gun 10 is generally supported by a mounting bracket 12. Included with this particular system are a solenoid 14, a syringe-type liquid cylinder 16, a needle valve assembly generally designated 20, and a magnetically-driven stirring assembly generally designated 50. Liquid cylinder 16 is secured and sealed to solenoid 14 with a TEFLON(copyright) cap 31. Cap 31 is attached to solenoid 14 by means of four machine screws 32 (only two of which are shown in FIG. 1). An O-ring 33 is fit into a groove of cap 31 located at the end of cap 31 most distal to solenoid 14. O-ring 33 seals cylinder 16 and maintains the dispensing pressure differential.
Needle valve assembly 20 includes an elongate pin or needle 22, a needle seat 24 and a needle seat holder 26. An outer gun casing 35 is coaxially disposed around liquid cylinder 16, and includes a lower cap 37 in which needle seat holder 26 and a nozzle 39 are disposed. A conical element 22A (also shown in perspective view in FIG. 3) is slid onto needle 22 such that it rests on the top surface of a suspension contained in cylinder 16. Conical element 22A prevents upward splashing of the suspension during agitation thereof, and also prevents evaporation of volatile media during agitation.
Stirring assembly 50 includes an external magnetic drive member or stirring ring 52 mounted coaxially around gun casing 35. Magnetic drive member 52 includes two diametrically opposed external magnets 54A and 54B, and is operatively connected to a pneumatic stirrer motor 56 through a coupling 58. Coupling 58 operates to transfer rotational force developed by stirrer motor 56 to rotational motion effected by stirring ring 52, such that external magnets 54A and 54B can rotate about the central longitudinal axis of metering gun 10. For example, coupling 58 could be a toothed gear which engages teeth on stirring ring 52. The position of motor 56 is determined by a mounting bracket 59. Stirring assembly 50 also includes a stirring element in the form of a magnetic stir bar 60, which has a dominant length along an axis transverse to the central longitudinal axis of metering gun 10. Magnetic stir bar 60 has a bore drilled therethrough, such that needle 22 extends through the center of magnetic stir bar 60 and the magnet therein. Importantly, magnetic stir bar 60 is by necessity supported by an O-ring 62.
In operation, cylinder 16 is filled with a suspension and secured to solenoid 14. Magnetic drive assembly 50 is activated such that external magnets 54A and 54B rotate around cylinder 16 and induce a magnetic coupling with magnetic stir bar 60. This in turn causes magnetic stir bar 60 to rotate about needle 22 to thereby agitate the suspension contained in cylinder 16 and prevent the suspension from separating in cylinder 16, such as by sedimentation or creaming. Needle 22 is used to meter suspension from cylinder 16. When needle 22 is seated in needle seat 24, metering gun 10 is closed. At predetermined intervals, however, solenoid 14 of metering gun 10 causes needle 22 to lift upwardly out of needle seat 24 to create a passage from cylinder 16 to nozzle 39, and a metered dose of the suspension can be dispensed through nozzle 39 under the influence of a pressure differential.
Some problems have been observed in the use of metering systems such as that described hereinabove. The configuration of stirring assembly 50 is such that O-ring 62 is needed to support the vertical position of magnetic stir bar 60 within cylinder 16 and needle 22 is needed to maintain a proper axis of rotation for magnetic stir bar 60. With repeated use of metering gun 10, O-ring 62 begins to loosen from its fixed position on needle 22 and slip downwardly towards the bottom of cylinder 16. This causes magnetic stir bar 60 to jam or seize against the inside surface of cylinder 16, thereby defeating the function of stirring assembly 50. On other occasions, either the weight of magnetic stir bar 60 on O-ring 62, the mass of magnetic stir bar 60, or the contact made between magnetic stir bar 60 and needle 22 causes downward and/or lateral forces on needle 22. Consequently, needle 22 is often deflected laterally and hence fails to seat properly onto needle seat 24 at the intended points of time, thereby causing a xe2x80x9cconstantly openxe2x80x9d malfunction. Alternatively, the forces imparted on needle 22 can cause needle 22 to become jammed in needle seat 24 such that the valve becomes clogged. These failure events have been observed to occur both sporadically and completely, and are believed to be due at least in part to the rocking of magnetic stir bar 60 back and forth at an angle to needle 22. In addition, the rapid vertical oscillation of needle 22 during high-frequency metering operations imparts a hammering effect on magnetic stir bar 60, causing stir bar 60 to move O-ring 62 downwardly.
An additional problem stems from the fact that a bore is drilled through magnetic stir bar 60 to enable needle 22 to pass therethrough. The drilling of the bore can produce residual ferromagnetic particles which, due to magnetic attraction, are difficult to identify and eliminate from the bore prior to installation of magnetic stir bar 60 in cylinder 16. These particles can contaminate the suspension, and additionally can cause seizing of stir bar 60 on needle 22.
The configuration of magnetic stir bar 60 is also believed to engender a further problem observed wherein portions of the suspension splash upwardly to regions of cylinder 16 from which the suspension cannot easily be extracted, especially when the height of the suspension falls down to or below the level at which stir bar 60 is operating.
It is also believed that the configuration of the stirring element could be improved over the current stir bar design in order to improve the ability to stir suspensions having broader concentration, viscosity and thickness ranges.
The present invention is provided to solve these and other problems associated with the operations of liquid metering systems.
According to one embodiment of the present invention, an agitator assembly for agitating a substance in a container comprises a container, a magnetic drive device, and an agitator element. The container has a central longitudinal axis and includes a lateral wall defining an inside wall surface and an outside wall surface. The magnetic drive device is disposed adjacent to the outside wall surface of the lateral wall. The agitator element is disposed in the container and is magnetically coupled with the magnetic drive device for self-supported rotation about the central longitudinal axis. The agitator element includes an agitator body, a first magnet mounted at the agitator body, and a second magnet mounted at the agitator body and circumferentially spaced from the first magnet. The agitator element substantially centered about the central longitudinal axis and supported at a substantially constant axial position within the container by the magnetic drive device.
According to another embodiment of the present invention, a fluid metering device comprises a container, an elongate valve member, and an agitator assembly including a drive device and a movable agitator element. The container has a longitudinal axis and includes a lateral wall and an outlet aperture. The elongate valve member extends into the container, and is movable substantially along the longitudinal axis to alternately open and close the outlet aperture. The agitator element includes surfaces adapted to agitate a substance contained in the container. The agitator element is disposed in the container in non-contacting relation with the valve member, and is supported at a substantially constant axial position within the container at a distance from the outlet aperture.
The present invention further provides a method for agitating a substance in a container. In the method, a container is filled with a substance such as a viscous or a concentrated suspension. A magnetic drive device is mounted at a position adjacent to a lateral wall of the container. An agitator element is constructed by forming an agitator body, mounting a first magnet to the agitator body, and mounting a second magnet to the agitator body in circumferentially spaced relation to the first magnet. The agitator element is then immersed in the substance. The agitator element is caused to maintain a vertically suspended position along a length of the container by establishing a magnetic couple between the magnetic drive device and the agitator element. The agitator element is caused to rotate about a central longitudinal axis of the container, while remaining substantially centered along the longitudinal axis, by rotating the magnetic drive device around the container.
It is therefore an object of the present invention to provide a stirring element which is self-supporting at a relatively constant vertical position within a liquid cylinder or other container without the need to make physical contact with additional support structure within such cylinder.
It is another object of the present invention to provide a stirring element which does not jam or seize against the cylinder or against a metering needle or other valve component provided with the cylinder.
It is a yet another object of the present invention to provide a stirring element which rotates around a central longitudinal axis of the cylinder in a substantially constant radial position with respect to such longitudinal axis, and which does not rely on the presence of a metering needle to maintain such position.
It is a further object of the present invention to provide a stirring element which does not impair and affect the oscillatory and seating operations of a metering needle or other valve component provided with the cylinder.
It is a still further object of the present invention to provide a stirring element which permits a higher stirring rate without shearing the magnetic couple produced between the stirring element and an external magnetic drive device driving the stirring element.
Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.